1. Field of the Invention
The present invention generally relates to an improved method for selectively treating wells using a low viscosity epoxy resin-forming composition. More particularly, the invention pertains to the use of a low viscosity epoxy resin-forming composition containing a single curing agent which polymerizes to an impermeable solid after a latent period under ambient conditions for downhole applications.
2. Description of the Prior Art
Various processes have been proposed in the patent literature for treating wells with epoxy resin-forming solutions in order to consolidate, isolate or strengthen permeable subterranean earth formations in or around the boreholes of wells. For instance, U.S. Pat. No. 3,933,204 to Knapp describes a well treating process in which a permeable region is plugged by injecting into the region an aqueous emulsion containing an epoxy polymer, an acrylic polymer and a material for controlling the rate of interaction of the two polymers. Another such procedure for utilizing a polymeric material within a permeable structure is set forth in U.S. Pat. No. 4,042,031 to Knapp, which discloses a method for plugging subterranean formations with aqueous epoxy emulsions containing fine solid particles. In addition, U.S. Pat. No. 4,074,760 to Copeland et al. describes an aqueous based slurry containing an epoxy resin, a curing agent, a solvent, a particulate material, a coupling agent and a surfactant for forming consolidated gravel packs. However, these aqueous polymeric emulsions are not sufficiently stable to be stored or transported without agglomeration and can not be easily prepared or handled in the field by the average well technician. Also, such aqueous systems suffer from the inability to form strong packs under a wide range of well conditions.
More recently, U.S. Pat. No. 4,921,047 to Summers et al. teaches compositions for use in sealing permeable subterranean formations which comprises a liquid epoxy material and two hardeners. It is stated that each of the hardeners has a different activation temperature and the hardening time of the epoxy material is of short duration under subsurface conditions of generally elevated temperature and pressure. However, the use of such epoxy formulations in certain well bore applications have inherent disadvantages. For instance, in shallow low temperature wells having a relatively reduced thermal gradient, the epoxy resin-forming compositions taught in the cited prior art may not be able to form a coherent structure of relatively high compressive strengths due to under-cured epoxy material at subsurface temperatures substantially below 170.degree. F., for example. A further disadvantage of such epoxy systems is that they become considerably more viscous at lower surface temperatures, e.g. below 75.degree. F., making them difficult to handle prior to and during placement of the epoxy material. To aid in mixing and handling these epoxy materials under such adverse conditions, the Summers patent suggests the need to preheat the epoxy systems above ambient temperatures. However, this preheating step can effect the fluidity of the epoxy material during placement and may result in uncontrollable set times. Also, operators at the well site are reluctant to use epoxy materials which require the selection of multiple thermally activated hardeners because of the safety risks involved in mishandling large quantities of these highly reactive materials. The energy released from exothermic epoxy reactions using inappropriate types or amounts of hardeners can produce extremely high temperatures which can damage underground equipment or adversely effect the physical properties of the resin product.